The present invention relates to tube repair, and more particularly to securing a bypass member or sleeve within a tube.
Nuclear power steam supply systems, particularly the pressurized water type, include a large steam generator heat exchanger having tube and shell sides separated by a thick tube sheet. A recurring problem has arisen with such steam generators in that defects eventually cause leakage of radioactive, primary water from the tube side to the secondary, relatively clean water of the secondary side. The radioactivity level of the secondary side must remain within strict limits and accordingly the leaking tubes must be repaired during plant outages.
A variety of techniques have been proposed for repairing such tubes, but few have proven satisfactory. It is preferred that the tubes be sleeved to enable continued opertion of the tube and thereby take advantage of the full heat exchange capacity of the steam generator. Although the plugging is more expedient and is sometimes undertaken where excess steam generator capacity is available or the plant outage is of short duration, sleeving is usually preferred.
A particularly advantageous tube repair technique is described in co-pending U.S. Ser. No. 477,292 U.S. Pat. No. 4,485,847, "Compression Sleeve Tube Repair", which discloses a plug embodiment and a sleeve embodiment, both of which include means for cooperating with the tube sheet lower surface to secure the plug or sleeve against the tube wall. Such sleeve is particularly adapted to repairing defects caused by sludge or crud deposits immediately above the tube sheet. The advantages incliude quick installation time and easy removal should such need arise subsequent to installation and use. Also, a constant preload under both hot and cold conditions is maintained as a result of the preferred use of the tube material for the repair sleeve. Presently, the sleeve technique disclosed in U.S. Ser. No. 477,292 is conveniently used when the defect is within abouyt three or four feet from the tube sheet.
Occasionally, defects occur in locations many feet above the tube sheet, where it may become impossible or impractical to secure a sleeve in the tube while taking advantage of the backup, strength or stop surfaces available on or within the tube sheet. Accordingly, a need has been identified, to obtain many of the advantages associated with the referenced disclosure, while having greater flexibility as to where the repair device can be located within the tube.